(Background of the Art) An electric double layer capacitor is one kind of a condenser in which an electrode is formed by providing an electrode active material layer on a metal foil collector, and a pair of the electrodes is wound around disposing a separator therebetween. It has a small scale with a large capacitance, endures overcharging and discharging, and also the load imposed upon the environment is small from the viewpoint of materials used. Conventionally, an electric double layer capacitor is used for backup of a memory of an electronic appliance such as a video or an audio apparatus, as an auxiliary power source at the time of replacing the cell in a portable appliance, or in a clock or a stored power source of a displaying lamp appliance by using a solar cell. In recent years, by utilizing the small scale, large capacitance and large electric current, the electric double layer capacitor is expected as a starting power source for a small motor or a cell motor of an automobile or an electronic appliance. For providing larger capacitance, an electrode is demanded that can contain more electrode active material in a predetermined volume.
(Prior Art) Conventionally, an electric double layer capacitor is known in which a polarized electrode formed by mixing activated carbon with an electrically conductive auxiliary agent and a binder and applying the mixture onto a collector made of aluminum foil or copper foil followed by drying and pressing to provide a higher density, is cut into a predetermined size to form electrodes, and a pair of the electrodes are wound disposing a separator therebetween and put into a predetermined cell container with an electrolytic solution (for example, see Japanese Patent Application Laid-Open (JP-A) Nos. Hei. 03-280518, Hei. 08-293443 and Hei. 08-107045). However, reduction of the thickness of the collector is already near the limit. Also, when the application amount of activated carbon per unit area of the electrode is increased in order to put more activated carbon into a cell container having a predetermined volume, the electric conduction path cannot be sufficiently ensured, so that the resistance increases, leading to a drawback such that it is difficult to increase the application amount while leaving a part on which tabs for taking electricity out are to be welded.
Also, those in which an electrode active material layer is formed on both surfaces of a collector are known (for example, see JP-A Nos. Hei. 08-990056 and 2000-202358). However, the electrode active material layer is applied in a stripe form in longitudinal direction and, though the width direction only can be adjusted, a different pattern cannot be provided on the front and the back, and the pattern is a limited one. Further, there is a drawback such that, when high pressure is received at the time of pressing, wrinkles are generated due to the difference in the thickness between the coated section having a stripe form and the non-coated section.
Therefore, the present invention has been made in order to eliminate such problems. An object thereof is to provide an electric double layer capacitor electrode having a low collector resistance and a high capacitance even when it is provided with an electrode active material layer containing more activated carbon, by forming the electrode active material layer in a pattern, as well as a method for producing the same and an electric double layer capacitor.